Tunable power amplifier with wide frequency range

ABSTRACT

A circuit includes an amplifier configured to amplify an input signal and generate an output signal. The circuit also includes a tuning network configured to tune frequency response of the amplifier. The tuning network includes at least one tunable capacitor, where the at least one tunable capacitor includes at least one micro-electro mechanical system (MEMS) capacitor. The amplifier could include a first die, the at least one MEMS capacitor could include a second die, and the first die and the second die could be integrated in a single package. The at least one MEMS capacitor could include a MEMS superstructure disposed over a control structure, where the control structure is configured to control the MEMS superstructure and tune the capacitance of the at least one MEMS capacitor.

TECHNICAL FIELD

This disclosure is generally directed to radio frequency (RF) poweramplifiers. More specifically, this disclosure is directed to a tunablepower amplifier with a wide frequency range.

BACKGROUND

A radio frequency (RF) power amplifier and its matching network aretypically designed for operation at a fixed carrier frequency. At othercarrier frequencies, the power amplifier often loses performance,including efficiency, output power, and linearity. For example, if apower amplifier loses linearity, it cannot satisfy its spectral maskrequirements, and pre-distortion is often needed, which in turn is morecomplicated, consumes more power, and occupies more die area.

For modern wireless communication systems where the frequency range ofinterest is very wide, multiple power amplifiers may be needed to coverdifferent frequency bands within the frequency range of interest.Unfortunately, using multiple power amplifiers can incur significantincreases in cost, complexity, power consumption and die area. Having asingle tunable power amplifier that can cover multiple frequency bandsis a more attractive solution for these applications.

SUMMARY

This disclosure provides a tunable power amplifier that covers a widefrequency range.

In one example, a circuit includes an amplifier configured to amplify aninput signal and generate an output signal. The circuit also includes atuning network configured to tune the frequency response of theamplifier. The tuning network includes at least one tunable capacitor,where the at least one tunable capacitor includes at least onemicro-electro mechanical system (MEMS) capacitor.

In another example, a method includes amplifying an input signal andgenerating an output signal using an amplifier. The method also includestuning frequency response of the amplifier using a tuning networkcoupled to the amplifier. The tuning network includes at least onetunable capacitor, and the at least one tunable capacitor includes amicro-electro mechanical system (MEMS) capacitor.

In a third example, a system includes an amplifier having multiple poweramplifiers. The system also includes a tuning network having (i)multiple inductors each coupled to one of the power amplifiers and (ii)multiple tunable capacitors coupled to the inductors. Each tunablecapacitor includes at least one micro-electro mechanical system (MEMS)capacitor.

Other technical features may be readily apparent to one skilled in theart from the following figures, descriptions, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure and its features,reference is now made to the following description, taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 illustrates an example digital light processing (DLP)micro-electro mechanical system (MEMS) tunable capacitor;

FIGS. 2A and 2B illustrate an example tunable power amplifier inaccordance with this disclosure;

FIGS. 3 through 10 illustrate example operational and other detailsregarding high-power and low-power implementations of the tunable poweramplifier in accordance with this disclosure; and

FIG. 11 illustrates an example of a tunable power amplifier in a packagein accordance with this disclosure.

DETAILED DESCRIPTION

FIGS. 1 through 11, discussed below, and the various examples used todescribe the principles of the present invention in this patent documentare by way of illustration only and should not be construed in any wayto limit the scope of the invention. Those skilled in the art willunderstand that the principles of the present invention may beimplemented in any suitable manner and in any type of suitably arrangeddevice or system.

As noted above, a radio frequency (RF) power amplifier and its matchingnetwork are typically designed for operation at a fixed carrierfrequency. Operations at other carrier frequencies or over a frequencyrange of interest can be problematic for conventional RF poweramplifiers. In accordance with this disclosure, a power amplifier isprovided on or over a die (such as a complementarymetal-oxide-semiconductor or “CMOS” die) and integrated with tunablecapacitors (such as micro-electro mechanical system or “MEMS”capacitors) and inductors in the same package. The MEMS capacitors areused to achieve higher amplifier performance and may be based on theDIGITAL LIGHT PROCESSING (DLP) technology from TEXAS INSTRUMENTS INC. ofDallas, Tex.

FIG. 1 illustrates an example DLP MEMS tunable capacitor 10. As shown inFIG. 1, the tunable capacitor 10 includes a superstructure having atleast one deflectable metallic membrane 12. Hinges 13 hinge the membrane12 over an underlying control section, which includes at least oneelectrode 14 formed over a substrate 16. A space D between the membrane12 and the electrode 14 forms a dielectric. A control voltage V+provided to the electrode 14 by a controller 18 creates an electrostaticforce on the membrane 12 that controllably varies the distance D betweenthe membrane 12 and the electrode 14 to establish a variablecapacitance. Each tunable capacitor 10 has two states, a highcapacitance state (minimum distance D between membrane 12 and electrode14) and a low capacitance state (maximum distance D between membrane 12and electrode 14). Thus, the capacitors 10 are bi-stable. Multiplecapacitors 10 combined together, such as in an array, provide a widetunable capacitance range that is obtained by controlling the states ofmultiple capacitors 10. A voltage may also or alternatively be providedto the membrane 12 to create the electrostatic force. The membrane 12can be substantially planar and substantially parallel to the electrode14 and move vertically to vary the distance D and thus the capacitance.

As described in more detail below, one or multiple MEMS capacitors 10are used in a power amplifier's tuning network. This is beneficial sinceMEMS capacitors provide high RF power handling capability, wide tuningranges, and good RF performances such as high quality factor, smallinsertion loss and high linearity compared to varactor diodes orordinary switched capacitor banks. MEMS capacitors can also be used insmaller packages. As particular examples, a tunable MEMS capacitor(array of MEMS capacitors 10) may have a tolerance of 0.1 pF, a Q>100 at1 GHz, and a Q>50 at 2 GHz, and the linearity may be IIP3>75 dBm. Thesevalues can help to achieve superior performance of a power amplifier atthese frequencies. For example, if the variable capacitor has a highinsertion loss, then the power amplifier loses output power andefficiency degrades.

In some implementations, the controller 18 provides digital levels ofthe control voltage V+ to individual MEMS capacitor 10 of a tunablecapacitor array so that the capacitance can be set in steps. Forexample, in some implementations, the capacitance of a tunable MEMScapacitor array can be programmed and digitally tuned in 0.17 pF stepsand have a range of 1 pF to 6.5 pF. Note, however, that other values andranges can be provided as desired.

FIG. 2A illustrates an example tunable power amplifier 20 in accordancewith this disclosure. In this particular example, the tunable poweramplifier 20 represents a tunable outphasing or LINC (LinearAmplification with Nonlinear Components) power amplifier, which could beformed at least partially on a CMOS die 22 or other semiconductor die.The tunable power amplifier 20 could have any suitable operatingfrequency range. For instance, the tunable power amplifier 20 couldrepresent a tunable outphasing power amplifier with an operatingfrequency range from 1.5 GHz to 2.7 GHz.

As shown in FIG. 2A, the tunable power amplifier 20 includes amplifiersections comprising four power amplifiers P₁-P₄, four inductors L₁-L₄,three tunable capacitors C₁-C₂ and C_(out), and a load resistor R. Thetunable capacitors C₁-C₂ and C_(out), along with inductors L₁-L₄, form atuning network 24 for the power amplifier. A first differentialoutphasing input signal S₁/S₁′ is coupled to the power amplifiers P₁ andP₃, and a second differential outphasing input signal S₂/S₂′ is coupledto power amplifiers P₂ and P₄.

Each of the power amplifiers P₁-P₄ represents any suitable type(s) ofswitching power amplifier(s), such as a class-D or class-E amplifier.Each of the inductors L₁-L₄ represents any suitable inductive structurehaving any suitable inductance. In some implementations, the inductorsL₁-L₄ have substantially equal inductances. Each of the tunablecapacitors C₁-C₂ and C_(out) represents any suitable tunablecapacitor(s), such as multiple MEMS capacitors 10 configured in parallelor other arrangement. In some implementations, the capacitors C₁-C₂ aretuned to have substantially equal capacitances. Note that each MEMScapacitor array forming the tunable capacitors C₁-C₂ and C_(out) couldhave its own controller 18, or multiple MEMS capacitor arrays formingthe tunable capacitors C₁-C₂ and C_(out) could share a common controller18. The load resistor R represents any suitable resistive structurehaving any suitable resistance.

FIG. 2B shows an example schematic of a frequency-tunable widebandclass-E outphasing power amplifier 20. Simulation results obtained fromthis design are shown in FIGS. 3-10. Each class-E power amplifier P₁-P₄consists of a core switching device (NMOS transistor N₂) that is drivenby the outphasing waveform through a driver chain 26, a high voltagecascode NMOS transistor (N₁) biased properly, which can sustain highervoltage stress and is used here to obtain higher peak output power fromthe outphasing power amplifier 20, a capacitor C_(P) (in this design noexternal capacitor is used, the output capacitance of the poweramplifier P₁-P₄ is used as C_(P)), and an inductor L_(C) which connectsthe power amplifiers P₁-P₄ to the power supply V_(DD). Inductors L₁-L₄and capacitors C₁ and C₂ are tuned for class-E operation. CapacitorC_(out) is the output capacitor connected to load resistance R through abalun T. Capacitors C₁-C₂ and C_(out) are built using tunable MEMScapacitors. The capacitors C₁-C₂ and C_(out) and inductors L₁-L₄ formthe outphasing combiner as well as the matching network.

In addition, LC circuits tuned to specific harmonic frequencies can beconnected between the drains of the cascode transistors N₁ ofdifferential sides for waveform shaping, and those capacitors are alsobuilt using MEMS and can be tuned over wide frequency range of interest.Inductors or capacitors can be connected between the drains of thecascode transistors N₁ of S₁ and S₂ sides for improving back-offefficiency.

FIGS. 3 through 10 illustrate example operational and other detailsregarding high-power and low-power implementations of the tunable poweramplifier 20 in accordance with this disclosure. More specifically,FIGS. 3 through 6 illustrate example operational and other detailsregarding the high-power implementation of the tunable power amplifier20, and FIGS. 7 through 10 illustrate example operational and otherdetails regarding the low-power implementation of the tunable poweramplifier 20. The tunable capacitors C₁-C₂ and C_(out) have a highercapacitance range (tuning range) in the high-power implementation of thepower amplifier 20 than in the low-power implementation of the poweramplifier 20. Both implementations of the power amplifier 20 cover thefrequency range from about 1.5 GHz to about 2.7 GHz in the examplesshown, although other frequency ranges could be used.

Parameters and results of the high-power implementation of the poweramplifier 20 are shown in FIGS. 3 through 6. FIG. 3 shows the values ofthe tunable MEMS capacitors C₁-C₂ as a function of the tuned frequencyof the power amplifier 20. The value of each MEMS capacitor C₁-C₂ isprogrammable between 35 pF and 70 pF. FIG. 4 shows the values of theMEMS capacitor C_(out) as a function of the tuned frequency of the poweramplifier 20, where the value of the MEMS capacitor C_(out) isprogrammable between 3.7 pF and 9 pF.

FIG. 5 shows the efficiency of the power amplifier 20 as a function offrequency, where the efficiency is relatively high and consistent overthe frequency range. FIG. 6 shows the output power of the poweramplifier 20 as a function of frequency, which again is relatively highand consistent over the frequency range.

Parameters and results of the low-power implementation of the poweramplifier 20 are shown in FIGS. 7 through 10. FIG. 7 shows the values ofthe tunable MEMS capacitors C₁-C₂ as a function of the tuned frequencyof the power amplifier 20. The value of each MEMS capacitor C₁-C₂ isprogrammable between 3 pF and 9 pF. FIG. 8 shows the values of the MEMScapacitor C_(out) as a function of the tuned frequency of the poweramplifier 20, where the value of the MEMS capacitor C_(out) isprogrammable between 3.2 pF to 8.5 pF.

FIG. 9 shows the efficiency of the power amplifier 20 as a function offrequency, where the efficiency is relatively consistent over thefrequency range. FIG. 10 shows the output power of the power amplifier20 as a function of frequency, which is relatively consistent over thefrequency range.

FIG. 11 illustrates an example of a tunable power amplifier in a package30 in accordance with this disclosure. The package 30 includes asubstrate 32 with the CMOS die 22 positioned on an upper surface 34 ofthe substrate 32. The CMOS die 22 includes the power amplifiers P₁-P₄shown in FIG. 2. The package 30 also includes the inductors L₁-L₄positioned proximate the CMOS die 22. The inductors L₁-L₄ are designedas spiral inductors using the metal layers of the package 30. Oneinductor L₁-L₄ is provided for each power amplifier P₁-P₄, respectively,as shown in FIG. 2.

Multiple MEMS modules 36 form each capacitor C₁-C₂, and one MEMS module36 forms the capacitor C_(out). Each MEMS module 36 could include threetunable MEMS capacitor banks coupled in parallel. The MEMS modules 36forming each capacitor C₁-C₂ are coupled in parallel so that all nineMEMS capacitor banks are coupled in parallel. Note, however, that thenumber of MEMS modules 36 and the number of MEMS capacitor banks in eachMEMS module 36 are for illustration only. Each MEMS module 36 caninclude a semiconductor die that is separate from the die 22.

In the illustrated example, the MEMS modules 36 are positioned on theupper surface 34 of the substrate 32 and are radially positioned aroundthe CMOS die 22. A controller 18 may be provided for each MEMS module 36to control the capacitance of that MEMS module 36, or a controller 18could be provided in the package 30 to control the capacitance ofmultiple MEMS modules 36. In any case, each of the MEMS modules 36 canbe digitally programmed by remote control signals provided to thepackage 30.

The capacitor C_(out) is positioned at a central portion of the package30 between the two capacitors C₁-C₂, which are positioned at opposingends of the package 30. The interconnects between the CMOS die 22, theinductors L₁-L₄, and the MEMS modules 36 can be formed by strip lines asthe package 30 may operate at frequencies over 1 GHz. The CMOS die 22 ispositioned in a central portion of the substrate 32 to help reduce orminimize distance, and thus associated parasitics, introduced by theinterconnects between the CMOS die 22 and the tuning network formed bythe inductors L₁-L₄ and the tunable capacitors C₁-C₂ and C_(out). Inputterminals of the power amplifier 20 can be formed proximate the CMOS die22 to reduce or minimize parasitics. The external control signals thatprogram the capacitors C₁-C₂ and C_(out) may be provided at any locationon the package 30.

In this example, three MEMS modules 36 form each MEMS capacitor C₁-C₂,and one MEMS module 36 forms the MEMS capacitor C_(out). Each MEMScapacitor C₁-C₂ is programmable, such as between 9 pF and 58.5 pF, andthe MEMS capacitor C_(out) is programmable, such as between 3 pF and19.5 pF. Note, however, that other values could also be supported. Also,in other embodiments, more or fewer MEMS modules 36 may be used to formthe programmable MEMS capacitors C₁-C₂ and C_(out) of the poweramplifier 20, where more MEMS modules 36 are used to create MEMScapacitors having a greater capacitance tuning range.

Although FIGS. 1 through 11 illustrate examples of tunable poweramplifiers that are operable over a wide range of frequencies, variouschanges may be made to FIGS. 1 through 11. For example, the tunablepower amplifier 20 could include any other suitable arrangement of poweramplifiers, inductors, capacitors, and resistors. The power amplifierscould comprise of other types, such as pulse width modulated (PWM) poweramplifier, linear power amplifiers etc and suitable tunable matchingnetworks can be designed accordingly. Also, each tunable capacitor C₁-C₂and C_(out) could be implemented using any number of MEMS capacitors,including a single MEMS capacitor or multiple MEMS capacitors placed inany suitable arrangement. In addition, the values shown in the graphs inFIGS. 3-10 are examples only. Other embodiments of the tunable poweramplifier 20 could have any other suitable operational characteristics.

It may be advantageous to set forth definitions of certain words andphrases used throughout this patent document. The terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation. The term “or” is inclusive, meaning and/or. The phrase“associated with,” as well as derivatives thereof, may mean to include,be included within, interconnect with, contain, be contained within,connect to or with, couple to or with, be communicable with, cooperatewith, interleave, juxtapose, be proximate to, be bound to or with, have,have a property of, have a relationship to or with, or the like. Thephrase “at least one of,” when used with a list of items, means thatdifferent combinations of one or more of the listed items may be used,and only one item in the list may be needed. For example, “at least oneof: A, B, and C” includes any of the following combinations: A, B, C, Aand B, A and C, B and C, and A and B and C.

While this disclosure has described certain embodiments and generallyassociated methods, alterations and permutations of these embodimentsand methods will be apparent to those skilled in the art. Accordingly,the above description of example embodiments does not define orconstrain this disclosure. Other changes, substitutions, and alterationsare also possible without departing from the spirit and scope of thisdisclosure, as defined by the following claims.

What is claimed:
 1. A circuit comprising: an amplifier configured toamplify an input signal and generate an output signal; and a tuningnetwork configured to tune frequency response of the amplifier, thetuning network comprising at least one tunable capacitor, wherein the atleast one tunable capacitor comprises at least one micro-electromechanical system (MEMS) capacitor.
 2. The circuit as specified in claim1, wherein: the amplifier comprises a first die; the at least one MEMScapacitor comprises a second die; and the first die and the second dieare integrated in a single package.
 3. The circuit as specified in claim1, wherein: the at least one MEMS capacitor comprises a MEMSsuperstructure disposed over a control structure; and the controlstructure is configured to control the MEMS superstructure and tune thecapacitance of the at least one MEMS capacitor.
 4. The circuit asspecified in claim 3, wherein the control structure is configured toelectrostatically control a position of the MEMS superstructure.
 5. Thecircuit as specified in claim 3, wherein: the control structurecomprises an electrode; and the MEMS superstructure comprises at leastone substantially planar membrane positioned parallel to the electrode.6. The circuit as specified in claim 1, wherein the at least one MEMScapacitor comprises multiple MEMS capacitors disposed along multiplesides of the amplifier.
 7. The circuit as specified in claim 1, whereinthe tuning network comprises multiple MEMS capacitors.
 8. The circuit asspecified in claim 1, wherein the amplifier comprises an outphasingamplifier including multiple amplifier sections each feeding arespective inductor, the respective inductors feeding the at least oneMEMS capacitor.
 9. A method comprising: amplifying an input signal andgenerating an output signal using an amplifier; and tuning frequencyresponse of the amplifier using a tuning network coupled to theamplifier, the tuning network comprising at least one tunable capacitor,the at least one tunable capacitor comprising a micro-electro mechanicalsystem (MEMS) capacitor.
 10. The method as specified in claim 9,wherein: the amplifier comprises a first die; the at least one MEMScapacitor comprises a second die; and the first die and the second dieare integrated in a single package.
 11. The method as specified in claim9, wherein: the at least one MEMS capacitor comprises a MEMSsuperstructure disposed over a control structure; and the controlstructure controls the MEMS superstructure and tunes the capacitance ofthe at least one MEMS capacitor.
 12. The method as specified in claim11, wherein the control structure electrostatically controls a positionof the MEMS superstructure.
 13. The method as specified in claim 11,wherein: the control structure comprises an electrode; and the MEMSsuperstructure comprises at least one substantially planar membranepositioned parallel to the electrode.
 14. The method as specified inclaim 9, wherein the at least one MEMS capacitor comprises multiple MEMScapacitors disposed along multiple sides of the amplifier.
 15. Themethod as specified in claim 9, wherein the tuning network comprisesmultiple MEMS capacitors.
 16. The method as specified in claim 9,wherein the amplifier comprises an outphasing amplifier includingmultiple amplifier sections each feeding a respective inductor, therespective inductors feeding the at least one MEMS capacitor.
 17. Asystem comprising: an amplifier comprising multiple power amplifiers;and a tuning network comprising (i) multiple inductors each coupled toone of the power amplifiers and (ii) multiple tunable capacitors coupledto the inductors, wherein each said tunable capacitor comprises at leastone micro-electro mechanical system (MEMS) capacitor in a package withthe amplifier.
 18. The system of claim 17, wherein: the tuning networkcomprises four inductors and three tunable capacitors; a first of thetunable capacitors is coupled to two of the inductors and a second ofthe tunable capacitors is coupled to two others of the inductors; and athird of the tunable capacitors is coupled between the first and secondtunable capacitors.
 19. The system of claim 17, wherein each of thetunable capacitors comprises multiple MEMS capacitors coupled inparallel, wherein each of the first and second tunable capacitors has alarger number of MEMS capacitors coupled in parallel than the thirdtunable.
 20. The system of claim 17, wherein the package has at leastone metal layer, and the inductors comprise spiral inductors comprisedof the at least one metal layer.